1. Field of the Invention
The present invention relates to a method for controlling the nozzle position in an ink-jet type image forming apparatus comprising nozzles for printing an image. More particularly, the present invention relates to a method for controlling the position of nozzles which move in relation to a print medium at the time of print-driving the image forming apparatus.
2. Description of the Related Art
Conventionally, image forming apparatus print an image on a print medium in response to print data input thereto, and, according to the type of printing, are classified into an ink-jet type which prints an image using an ink-jet process, and an electrophotographic type which prints an image using an electrophotographic process. Among these types, ink-jet type image forming apparatus are those for printing images by directly ejecting ink onto a print medium, as found in an ink-jet printer and a plotter.
Referring to FIG. 1 which shows a conventional ink-jet printer, an ink-jet type image forming apparatus 100 comprises a printing engine 130 for printing an image on a print medium P (see FIG. 2), a paper feeding device 120 for containing plural print mediums and for feeding the print mediums sheet by sheet while the image forming apparatus is print-driven, a paper transfer device with a plurality of rollers 151 and 153, and a control section (not shown) for controlling the respective driving sections for the above-mentioned devices. The printing engine 130 comprises a reciprocating carriage 131 installed within a printer body 110, one or more ink cartridges 133 for containing ink which are removably mounted in the carriage 131, and one or more nozzle plates 135 (see FIG. 2) for ejecting ink onto a print medium P. Each nozzle plate 135 is provided with a plurality of nozzles (not shown) for ejecting ink. For reference, an image forming apparatus for printing a multi-colored image may comprise a plurality of such cartridges and nozzle plates, wherein the number of cartridges and nozzle plates corresponds to the number of colors required for printing such an image. In addition, a nozzle plate 135 may be formed integral with an ink cartridge 133 as shown in FIG. 2, or integral with a carriage 131, although not shown in the drawings. Symbols S and B, which are not specifically described herein, respectively designate a guide shaft S and a belt B for guiding the movement of the carriage 131.
The image forming apparatus 100 configured as described above further comprises a detection sensor 137 for detecting an edge PE of a print medium at the time of print-driving as shown in FIG. 2. The detection sensor 137 is used for determining a size of a print medium, determining a blank space in a print medium corresponding to a size of an image to be printed, and controlling a nozzle position in relation to a print medium. For such a detection sensor 137, an optical detection sensor is generally used, which comprises a light source (not shown) and a light receiving part (not shown).
The positional information detected as described above is provided by the detection sensor 137 with respect to an edge PE of a print medium. Accordingly, the distances D1 and D2 of the detection sensor 137 from the nozzle plates 135, which are preset at the time of fabricating an image forming apparatus, are set as reference information, and the positions of the nozzles in relation to a print medium P are then monitored by combining the positional information of the detection sensor 137 measured in relation to the print medium P, and the reference information.
However, if the distances D1 and D2 between the nozzle plates 135 and the detection sensor 137, which are preset at the time of fabricating such an image forming apparatus, are used as reference information as described above, several problems can exist in that it is difficult to acquire accurate positional information for the nozzles. Such difficulties can be due to manufacturing tolerances, center deviations D3 between the detection sensor 137 and an effective detection area A, wherein the effective detection area A is a detected area practically detected by the detection sensor 137, variations of the distances D1 and D2 caused by any change in operating circumstances of the image forming apparatus, and replacement of the ink cartridges 133, or the like.
To this effect, other problems can then arise because the nozzle position is inaccurately controlled, such as the quality of print may become deteriorated and images may not be accurately adjusted and printed to a size corresponding to a blank space of a print medium as demanded by a user.
Accordingly, a need exists for a method to control nozzle position in relation to a print medium which can further compensate for variations, such as manufacturing tolerances, the replacement of articles of consumption such as ink cartridges, and any changes in operating circumstances of the image forming apparatus, to thereby prevent the quality of images from being deteriorated.